Chloranil test

A test for secondary amines (e.g. proline) is the Chloranil test (1 drop of a 2% acetaldehyde solution in DMF, followed by one drop of a 2% solution of p-chloranil in DMF, leave for 5 mins). A positive test gives blue stained beads. 

Two acylation reactions as depicted in Schemes 12.7 and 12.8 had the same issue when monitored by single bead FTIR (Fig.s 12.11 and 12.12). The starting resins (13) and (15) did not have convenient signal to monitor by FTIR. A chloranil test [15] specific for the secondary amines was used to confirm the complete consumption of (13), therefore the reaction completion. An iron-chloride-pyridine test [16] was used to confirm the complete consumption of (15). In both color tests, a blue color would suggest the presence of the starting material. In both cases we observed the disappearance of the blue color that indicated the reaction completion. 

The most popular test for the presence or absence of free amino groups is the Kaiser test.10 The test is simple and quick however it should be noted that some deprotected amino acids do not show the expected dark blue color typical of free primary amino groups (e.g., serine, asparagine, aspartic acid).11 Furthermore, for secondary amines such as proline, the resin will turn brown instead of blue. For secondary amines and aromatic amines, the chloranil test is recommended.12 In this volume, Albericio s research... 

Fmoc-amino acid coupling (resin 85) A solution of the requisite Fmoc-amino acid (1.5 mmol, 10 equiv.), TFFH (1.5 mmol, 10 equiv.), and DIEA (3.0 mmol, 20 equiv.) in dry DCE (7 ml) was added to the resin 84 (0.50 g, 0.15 mmol, 1 equiv.) and the suspension was shaken at rt for 2 days. The progress of the reaction was monitored by means of a modified chloranil test... 

Procedure for the CMoranil Test [237]. For Pro and other secondary amines, the chloranil test can be used [237]. Chloranil (2,3,5,6-tetrach-loro-1,4-benzoquinone) reacts with secondary and primary amines in the presence of acetone or acetaldehyde, respectively, to give a green-blue ben-zoquinone derivative. 

Acetaldehyde/chloranil test, a monitoring method for the control of complete coupling reaction in solid-phase peptide synthesis [T. Voikovsky, Peptide Res. 1995, 8, 236]. 

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